1. Field of the Invention
The present invention relates to a mixed-bed device of the non-regeneration type for producing pure water for use in the manufacture of electronic parts, pharmaceuticals, etc. by removing salts, free acids, bases and the like from a supply of water. The term "mixed-bed device for producing pure water" herein used refers to a device of the above-mentioned type.
2. Description of the Prior Art
The container of a mixed-bed device for producing pure water is filled with grains (for example of ion exchange resin) for forming pure water from usual water or like starting water. Starting water is supplied to an upper portion of the container under pressure and processed into pure water while flowing though the granular material toward the bottom of the container. The pure water is collected via a water collecting tube inserted into the container through an upper opening of the container.
With reference to FIGS. 15 and 16, water collectors for conventional mixed-bed devices for preparing pure water comprise a water collecting tube 105 directly formed in its lower end portion with a multiplicity of water collecting apertures in the form of slits 108 having a width smaller than the grain size of the granular material (FIG. 15), or a perforated strainer 108' attached to the lower end of a water collecting tube 105 and having a Saran net wound therearound (FIG. 16). In either case, the water collector is disposed at only one location in the inner lower portion of the container, for example, at the center.
Accordingly the starting water supplied under pressure to an upper interior portion of the container through an inlet tends to flow the shortest distance between the container upper portion and the water collector due to the resistance to the flow. Consequently the zone of contact between the starting water flowing toward the water collecting portion and the granular material is in the form of a cone having the base at the interior upper portion of the container and the vertex at the water collecting portion. We have found it impossible, for this reason, to effectively use the whole amount of granular material charged in the container and therefore to achieve a high pure water collection efficiency because of a limitation on the amount of pure water that can be collected with a single charge of granular material. We have further found that the starting water tends to remain between the grains which are positioned outside the contact zone, consequently promoting growth of a large amount of bacteria.
Furthermore, the position of the water collector which is limited imposes a limitation on the sum of aperture areas to give great resistance to the collection of water, consequently necessitatng a pump of increased discharge pressure and pressure-resistant container and parts.